The present invention relates to operation control methods for washing machines, and more particularly to a dehydrating method (spin-cycle control method) for washing machines.
The basic construction of a washing machine of the type to which the invention pertains will be described with reference to FIG. 1, which is a sectional side view of the washing machine. The washing machine shown is of the fully automatic, single-tank agitation type. In FIG. 1, reference numeral 1 designates an agitator composed of a hollow cylinder in which are formed a number of through-holes 2 and which has several agitator blades 3 secured to the outer wall of the cylinder extending vertically and arranged radially, and reference numeral 4 designates a dehydrating (spin) tank having the agitator 1 at its center. Through-holes 5 are formed in the side wall of the dehydrating tank 4. A balancer 6 including a hollow annular member is formed at the upper end opening of the dehydrating tank 4. The balancer 6 is used to prevent vibration of the dehydrating tank during dehydration. Further in FIG. 1, reference numeral 7 designates a water receiving tank provided outside the dehydrating tank 4, the tank 7 having a water discharging outlet (not shown) to which a drain pipe (not shown) is connected.
In FIG. 1, reference numeral 8 designates an electric motor which is coupled to a rotation transmitting section 12 through a speed reducing mechanism including a pulley 9, an endless V-belt 10, and a pulley 11. The rotation transmitting section has dual drive shafts 12a and 12b which are controlled by a spring clutch mechanism 13. The outer drive shaft 12a is coupled to the dehydrating tank 4, and the inner drive shaft 12b to the agitator 1.
The above-described mechanisms are all installed through a vibration preventing buffer (not shown) in the outer casing (not shown). A control device using a microcomputer and an operating section including operating switches are provided on the upper part of the outer casing. The outputs of a water level detector and other detectors are applied to the control device. The outputs of the control device are applied to a drive circuit for the motor 8, a valve control circuit for a water supplying valve, a water discharging valve, and other circuits.
In washing, rinsing and dehydrating operations with the washing machine, the clothes to be washed (the load), water and detergent are put in the tank 4, and then the power switch is turned on. As a result, the motor 8 is rotated alternately in the forward direction and in the reverse direction, and accordingly the agitator is rocked to effect washing. As controlled by a timer in the control device, the washing operation is continued for a predetermined period of time, whereupon the water is discharged. Thus, the washing cycle has been accomplished, and the dehydrating (spin) cycle is carried out.
In the dehydrating cycle, the spring clutch mechanism 13 is operated to rotate the shaft 12b together with the shaft 12a. The motor 8 is rotated in one direction only so that the dehydrating tank 4 is rotated through the pulley 9, the V-belt 10, the pulley 11, and the rotation transmitting section 12 by the motor 8. In this case, the speed of rotation of the dehydrating tank 4 is determined by the speed reduction ratio of the pulleys 9 and 11, and the speed of rotation of the motor 8 is determined from the number of poles. In the case of an induction motor, the steady-state speed of rotation is 900 rpm. When the speed of rotation reaches this value, the dehydrating operation is started.
In the above-described conventional dehydrating method, the rotation of the dehydrating tank is such that immediately after the rotation of the dehydrating tank is started, the speed of rotation of the tank quickly reaches a high speed of rotation of 900 rpm. Therefore, a high centrifugal force is abruptly applied to the wet clothes in the tank 4, which tends to shift the latter to one side of the tank 4, as a result of which the dehydrating tank strongly vibrates and produce large amounts of noise. Such vibration cannot be completely absorbed by the balancer 6 provided at the upper end opening of the tank 4.
The dehydrating tank 4 may be intermittently rotated merely by controlling the period of energization of the motor 8. However, since the force of rotation due to inertia depends on the weight of the load (the wet clothes), it is impossible to achieve accurate speed control with this method.
On the other hand, the dehydrating tank of a fully automatic washing machine in which the dehydrating tank is used as the washing tank also is larger than that of a double-tank type washing machine in which a washing tank is provided separately from the dehydrating tank. Therefore, the noise output and vibration of the former are generally larger than of the latter. In order to minimize the amount of noise and vibration, a balancer for causing the dehydrating tank to rotate in a horizontal plane is provided at the upper end opening of the dehydrating tank; however, a balancer cannot sufficiently eliminate the production of noise and vibration.
Recently, thin fabrics and delicate fibers such as wool are often washed in a home washing machine. In the conventional dehydrating operation, only one speed of rotation, which is considerably high (900 rpm), is provided. If woolen clothes are washed in such a machine and dried in a dehydrating tank which is rotated at such a high speed, an excessively high centrifugal force tends to be applied. As a result, the clothes can be excessively dehydrated and damaged or creased. This difficulty cannot be eliminated even if the period of dehydration is decreased or the dehydrating tank is intermittently rotated utilizing a timer.